1. Field of the Invention
The disclosed invention relates to a simplified acceleration aiding mechanization for electro-optical tracking of a designated target.
2. Description of the Prior Art
A number of airborne, electro-optical tracking systems have been developed which designate a target by reference to the line-of-sight of a television camera or a forward looking infrared camera as determined by a gimbaled optical sensor controlled by azimuth and elevation servos. The azimuth and elevation servos have been controlled either manually, by using a tracking control handle to center the target in a video display, or automatically, by using an automatic tracking sensor such as a video tracker or laser spot tracker. In the prior art tracking mechanizations, the manual tracking control handle or automatic tracking sensor controls azimuth and elevation non-linear gain amplifiers associated with parallel integrator-amplifier combinations to provide azimuth and elevation rate error signals. Conventional computations are performed on the aircraft velocity and attitude signals from the aircraft inertial navigation system and on range signals from a slant range sensor to provide azimuth and elevation rate aiding signals. The azimuth and elevation rate error signals are added to the computed azimuth and elevation rate aiding signals to provide azimuth and elevation rate command signals to control the respective azimuth and elevation servos of the gimbaled sensor.
In either the manual or automatic tracking mode of the prior art, the computed line-of-sight rate aiding signals, compensate for the motion of the aircraft relative to the target, thereby significantly improving tracking accuracy in a dynamic situation. It has been substantiated that dynamic tracking accuracy depends primarily upon the magnitude of the line-of-sight angular rotation rate and angular acceleration; upon the accuracies of the computed line-of-sight rate aiding signals, and upon the control authority given to the manual tracking control handle or the automatic tracking device. The availability of accurate rate aiding signals reduces the range of control authority required for the manual control handle or the automatic tracking device, thereby improving tracking accuracy by limiting threshold noise and/or manual and automatic overcontrol degradations. In the manual system, accurate rate aiding signals also ease the operator's control task and improve his learning curve.
If the computed rate aiding signals are accurate, the operator's tracking task is relatively simple and tracking accuracy is well within acceptable tolerances. However, as rate aiding accuracy degrades, tracking errors increase and tend to peak at maximum velocity/height (V/D) flyover conditions. For example, a simulated ten percent aiding error roughly triples the tracking inaccuracy at a flyover (V/D) of 0.2 sec. .sup.-.sup.1. On an aircraft not equipped with an inertial navigation system, or on which the inertial navigation system becomes inoperative, the azimuth and elevation rate aiding signals cannot be provided by the conventional computations. Without rate aiding for at least the elevation servo, the operator's control authority and the operator's human reflexes have proved inadequate to compensate for dynamic errors in tracking the target. Therefore, there was a need for a device which would provide elevation rate aiding for austere aircraft not equipped with an inertial navigation system. Additionally, in those aircraft equipped with inertial navigation systems, there was a need for a tracking aiding device which would produce elevation rate aiding signals in the event that the inertial navigation system of the aircraft became inoperative.